Problem: If $a + b = 2$ and $x + y + z = -4$, what is $-10x - 10y - 10b - 10a - 10z$ ?
Explanation: $= -10a - 10b - 10x - 10y - 10z$ $= (-10) \cdot (a + b) + (-10) \cdot (x + y + z)$ $= (-10) \cdot (2) + (-10) \cdot (-4)$ $= -20 + 40$ $= 20$